1. Field of the Invention
The present invention relates to a semiconductor system for a current sensor in a power semiconductor, e.g., for a power semiconductor of the type of a bipolar transistor having an insulated gate electrode, which is also called an insulated gate bipolar transistor (IGBT).
2. Description of the Related Art
Power semiconductors are usually manufactured as a vertical structure and have a plurality of transistor cells. In the process, gate and emitter structures are formed on the front side of a semiconductor substrate, which are connected via at least one p-n junction to the collector layer developed on the back side as a metallic coating over the entire surface. In power transistors, this cell structure is repeated over a large region of the substrate such that high currents may be transmitted. In so doing, care must be taken, however, to avoid short circuit states or overload states. Thus it is known from the general related art to attach a shunt resistor on the output terminal in order to detect possibly occurring short circuits or overload states in the primary current circuit.
The related art also teaches to branch off a region of the emitter or a portion of the emitter cells via a sensor terminal and to utilize the current flowing there as a signal. The sensor terminal is typically located within the emitter region and is entirely or partially filled with emitter cells. In the case of complete filling, the embedding of the sensor cells in the main emitter is very tight and it is to be expected that the behavior of the sensor cells deviates only slightly from that of the main emitter cells. Because of the relative sizes of the emitter terminal and the sensor terminal, however, a fixed ratio of sensor current to primary current is predefined. The case of a merely partial filling offers the advantage of being able to design this ratio more freely, but the tight embedding is lost and there are cell-free regions in which a charge carrier plasma likewise builds up in the conductive state.
When using or even already when designing an IGBT, care must be taken so that the charge carriers running off through the emitter in the switch-off case do not overload the individual transistor cells. In the example of an IGBT having an n channel, the charge carrier species running off through the emitter is provided by holes. The danger of overloading and the triggering of a latch-up exists specifically for the cells located on the edges of the sensing region and the main emitter region since a charge carrier plasma forms also in the cell-free regions without emitter contacts. This intermediate region that contains no cells (cell-free region) exists on the one hand when the sensor terminal is incompletely filled, although it also results from the necessity of having to separate the conductive layers connected to the two emitter regions.